Low-temperature synthesis of apatite-type La_9.33Ge₆O₂₆ as electrolytes with high conductivity

In the present study, high-quality apatite-type La_9.33Ge₆O₂₆ powders are successfully synthesized by a facile molten-salt synthesis method (MSSM) at low temperatures, using LiCl, LiCl/NaCl mixture (mass ratio 1:1) as molten salt, respectively. Experimental results indicate that the optimal mass ratio between reactant and molten salt is 1:2, and LiCl/NaCl mixed molten-salt is more beneficial for forming high-quality La_9.33Ge₆O₂₆ powders than LiCl individual molten-salt. Comparing with the conventional solid-state reaction method (SSRM), the synthesis temperature of apatite-type La_9.33Ge₆O₂₆ powders using the MSSM decreases more than 350℃, which can effectively avoid Ge loss in the preparation process of precursor powders. Furthermore, the powders obtained by the MSSM are homogeneous, non-agglomerated and well crystallized, which are very favorable for gaining dense pellets in the premise of avoiding Ge loss. On the basis of high-quality precursor powders, the dense and pure ceramic pellets of La_9.33Ge₆O₂₆ are gained at a low temperature of 1100℃ for 2 h, which exhibit higher conductivities (σ _850℃(LiCl)=2.3×10^-2 S·cm^-1, σ _{850℃(LiCl/NaCl)}=4.9×10^-2 S·cm^-1) and lower activation energies (E_a(LiCl)=1.02 eV, E_a(LiCl/NaCl)=0.99 eV) than that synthesized by the SSRM.